High burning rate propellants are generally formulated with very fine oxidizer particle sizes; however, the very fine particle sizes (20 micrometers) results in decreased usable potlife. Potlife refers to the time that the propellant can be stored before its viscosity becomes too high for it to be readily cast into a rocket motor. An alternate definition for a usable potlife is the time available for accomplishing the processing steps of mixing and casting a propellant composition before the propellant composition loses its fluid nature.
Aziridine compounds and adducts thereof have been effective in extending potlife. For example, U.S. Pat. No. 4,019,933, issued on Apr. 26, 1977 to Marjorie T. Cucksee et al. and assigned to the United States of America as represented by the Secretary of the Army, Washington, D.C., discloses trisaziridinylphosphine oxides adducts formed by reacting these oxides or their derivatives with monofunctional carboxylic acids.
To provide a better understanding of a number of compounds disclosed by U.S. Pat. No. 4,019,933, applicant presents structure VI, VII, and VIII from Column 3 and 4 of the above patent and which are referred to as HX874,HX868, and PEA respectively, as follows:
The compounds which are trisazirdinyl derivatives of triazine (represented by structure VI), the trisaziridinyl derivatives of benzenetriacyl (represented by structure VII), or N-phenethylaziridine (represented by structure VIII) are equally effective in extending the useful pot life of propellant mix. ##STR1## Wherein X.sub.1, is an aziridine group: ##STR2## and Q.sub.1, and Q.sub.2 are either hydrogen or alkyl groups of one to four carbon atoms. ##STR3## wherein X.sub.1 is as described for structure VI. ##STR4##
The cure catalysis function of ammonium perchlorate in propellants is believed to be related to the effective surface area of the ammonium perchlorate; the greater the surface area, the faster the curing rate with a corresponding increase in viscosity in a shorter time period of mixing. Thus, the coating of the fine ammonium perchlorate with the adducts formed from reacting aziridinylphosphine oxide with the monofunctional carboxylic acids inhibits or prevents the catalysis of the urethane type reaction (isocyanate-hydroxyl reaction) thus greatly extending the potlife, the time available for processing and casting propellant. The measurement of potlife can be related to vicosity measurements. The viscosity measurement on a Brookfield viscosimeter is arbitrarily set at the time it takes for the viscosity to reach 40 kilopoises.
The desire to control potlife during propellant processing is a motivative stimulus to the artisan. Not only is a propellant composition's useful life important in processing and casting to save mixing time and energy, but the useful life as determined by potlife can have major effects on the properties of the cured propellant, particularly, in the control of voids and maintaining homogeneity of the propellant ingredients in the cured propellant grain.
A compound which can control potlife and which contains a fuel contributing ingredient is recognized for its multifunctional properties and benefits.
Therefore, an object of the invention is to provide a method of controlling the increase in potlife of propellants during processing.
Another object of this invention provide a compound which after being incorporated into a propellant composition, the rate of viscosity increase is slowed by inhibiting the polymerization reaction in the propellant mix.